I would not consider going back to a returnless system over the simple and reliable returnless setup. Malcolm did alot of testing and posted it on another forum. Removing the regulator from the engine bay significantly reduces fuel temps, also dead head with a crossover works. My tuner confirms that my fuel pressure, cold and hot starts are solid. My hot starts adds maybe a second or two to cranking but nothing crazy that i would call a problem.

In reference to Vacuum / boost pressure vacuum line signal of course shorter is better but I think a long reference line that Ed is talking about would be something crazy long like to the trunk. I used a -4 teflon lined manifold reference line to my regulator. I'll never worry about it cracking, deforming or causing issues like rubber/silicone. A-little overkill but it gives me peace of mind. Again my tuner (Kevin Dunn aka 04sleeper) has nothing bad to say about the way I set everything up. He has stopped tuning in the past until i worked out issues.

I run an -8 feed/return with a -6 crossover. It may even be a -4 crossover, id have to look. Either way -4 or 6 for the crossover will work as it is just equalizing the two rails. This is if you go aftermarket rails.

Pressure drop between pump and rails would have me checking the fuel filter. It could be clogged or restrictive from the start. I run a fore filter with a pressure gauge on it and another gauge at the rails so i can check pressure drop indicating a clogging filter. Just a thought.

Another thing that will cause pressure variances, and the reason I am reference line length and diameter sensitive Troy, is a delay in signaling manifold pressure / vacuum to the regulator. The longer and thinner the line the more pronounced the manifold pressure signal delay and attenuation. Because the pressure regulator is boost or more accurately manifold pressure referenced you want to be able match it's fuel delivery to the engine's air appetite as closely as possible.

The extreme example is sucking air through a long straw as opposed to just taking a deep breath of ambient air. We want the FPR to be as close to being in lockstep with engine air appetite as possible. The best way to do this is to mount the FPR boost reference port directly to the intake manifold. In the real world this is obviously not practical so we use some type of conduit which turns out to be a rubber hose.

In an ideal build the rubber hose would be short enough and large enough in diameter to immediately adjust FPR fuel pressure. In the real world we have compromises we need to make. My best suggestion is make the line as short as practical and a reasonable enough diameter that the regulator does not behave like it is at the end of a long straw.

Sometimes end points or if you will extremes make some phenomena easier to visualize. If our reference line were very short but very large in diameter, the signal to the FPR could still be late. An endpoint type example would be a reference line with the same volume as the intake manifold. The FPR would still get the signal but it would be characterized by a delayed arrival, because of tube volume, and a muted signal strength again because of tube volume. At the other end of the pendulum swing a long skinny tube would also deliver a late and muted strength signal but for a different set of reasons.

By experimenting with tubing diameter and length while logging fuel pressure along with changes in TPS signal you can do a pretty good job of optimizing boost reference line metrics for your particular FPR placement so as to produce the most responsive FPR line pressure changes for TPS signal changes.

Another item sometimes removed in a conversion to a return style system is the FRPS. The OEM ECU uses this sensor to accurately calculate injector pulse widths based on measured delta pressure across the injector. It is definitely to anyone's advantage who switches to return style to maintain this sensor and it's interaction with the OEM ECU.

I’ve finished plumbing the -8 supply and feed lines. Finally setup the laptop to datalog, although I’m still not setup for AFR. Waiting for sensor bung to show up.

I drove it and it’s definately better. Although I’m still concerned that I might need a tune as it does behave a little differently. The idle is smoother. With the regulator on the rail, I’d have occasional misses at hot idle. Also, holding 1st or 2nd at 1500 to 2000 is smoother. It used to buck a little in that scenario. Any explanation for those?

Didn’t go full throttle but snapped it to 1/2 in 3rd gear. Made 9 psi and engine felt good. Looking at the data log (FRPS),pressure dropped about 3 psi from base, but recovered to 1 below base. I’m assuming I’m good here?

Couple questions:

1) How much run time is needed for long term fuel trims to be valid? Mine stayed at 1.00 throughout the log.

2) What’s normal behavior for short term trims? Mine fluctuated, high of 1.16, low of 0.81. Avg for log was 1.00.

3) At times, there is a squealing sound from the regulator. Mostly when at idle. I’d here the same sound, louder and more frequent, when the regulator was in the old location. Is this an issue? Normal?

1) Your long term fuel trims shouldn't take too long to start showing values. I typically see these within a drive cycle or two. If you're working on dialing in your tune, you should have "adaptive learning" off, which would disable your LTFTs (always 1.00)

2) Normal behavior is 1.00 +/- .05 and within .05 of each other. In my personal experience (twin turbo), these have been known to drift around on me at idle. With a little bit of throttle, they stable out.

3) As for the noise on the regulator, I won't be much help as mine has never made any noise (Magnafuel). Now, mine does come apart quite easily, and I've had it apart a few times just to ensure it was clean in there due to sitting for so long. You could try that. I'm not sure who makes your regulator, but you could call the manufacturer and see if they have any pointers on how to correct the issue you're having as well.

I drove it and itís definately better. Although Iím still concerned that I might need a tune as it does behave a little differently. The idle is smoother. With the regulator on the rail, Iíd have occasional misses at hot idle. Also, holding 1st or 2nd at 1500 to 2000 is smoother. It used to buck a little in that scenario. Any explanation for those?

Didnít go full throttle but snapped it to 1/2 in 3rd gear. Made 9 psi and engine felt good. Looking at the data log (FRPS),pressure dropped about 3 psi from base, but recovered to 1 below base. Iím assuming Iím good here?

I apologize, I missed these two questions.

1) In theory, as long as the fuel pressure drop at the injectors is the same, you should not require any adjustments to the tune. Also in theory, as long your FRPS is functioning properly and the tune is set accordingly, a small change in fuel pressure will be compensated for via a change in the injector pulse-width. Of course, the one who writes the checks if something is damaged due to improper fueling is you, not me, so take that as you will.

2) A change in fuel pressure on the hit is very normal. A reduction in pressure is also normal, and even more-so in most cases (bigger feed line vs smaller return line). If you really just snapped to 1/2 throttle, you haven't given the regulator a chance to do it's job and stabilize. From the sounds of it though, it seems as if everything is working correctly.

I would definitely recommend going to a tuner and having everything verified (or even better, tune it yourself). These cars are not very fun when you're worried about cooking a piston every time you hammer on it. Do eveyrthing you can to set yourself up for success, and hope the parts stay together.

Your squealing sound might just be the sound of the fuel returning over the edge of a sharp machined surface in the FPR and producing the squeal, sort of like when air leaks out of a balloon through a small orifice.

1) Your long term fuel trims shouldn't take too long to start showing values. I typically see these within a drive cycle or two. If you're working on dialing in your tune, you should have "adaptive learning" off, which would disable your LTFTs (always 1.00)

2) Normal behavior is 1.00 +/- .05 and within .05 of each other. In my personal experience (twin turbo), these have been known to drift around on me at idle. With a little bit of throttle, they stable out.

3) As for the noise on the regulator, I won't be much help as mine has never made any noise (Magnafuel). Now, mine does come apart quite easily, and I've had it apart a few times just to ensure it was clean in there due to sitting for so long. You could try that. I'm not sure who makes your regulator, but you could call the manufacturer and see if they have any pointers on how to correct the issue you're having as well.

1) I bet you’re right. Adaptive must be turned off in the current tune. I logged on the way to work, which included 2 stops along the way. Total of 3 ignition cycles and 30 minutes of driving.

2) The STFT numbers in my first reply were just the max min and avg. Remembering how Eric Brooks had me do a precious tune, holding at specific rpm points, I looked at STFT again at a few places when the RPMs were steady state. Both were around 1.05 and 1.10.

Originally Posted by smashedheadcat

I apologize, I missed these two questions.

1) In theory, as long as the fuel pressure drop at the injectors is the same, you should not require any adjustments to the tune. Also in theory, as long your FRPS is functioning properly and the tune is set accordingly, a small change in fuel pressure will be compensated for via a change in the injector pulse-width. Of course, the one who writes the checks if something is damaged due to improper fueling is you, not me, so take that as you will.

2) A change in fuel pressure on the hit is very normal. A reduction in pressure is also normal, and even more-so in most cases (bigger feed line vs smaller return line). If you really just snapped to 1/2 throttle, you haven't given the regulator a chance to do it's job and stabilize. From the sounds of it though, it seems as if everything is working correctly.

I would definitely recommend going to a tuner and having everything verified (or even better, tune it yourself). These cars are not very fun when you're worried about cooking a piston every time you hammer on it. Do eveyrthing you can to set yourself up for success, and hope the parts stay together.

1) I’ve had the same thought. Yes both configurations have 50 psi across the injector but then I realized that there is a key difference. With the regulator at the end of the rail, the pressure delta is 50, but the fuel is flowing through the rails rather quickly since the regulator (return) is at the end of the rails. With the dead head, pressure is still 50, but fuel flow should be much less than before (not counting WOT), since the regulator is now before the rails.

2) Sounds like I’m good from a pressure stand point, even though changes to the tune still might be necessary. That’s one of the reasons I moved the regulator. I knew I was heating the fuel and have been concerned about losing octane rating.

Originally Posted by eschaider

+1 on everything Josh said, Todd.

Your squealing sound might just be the sound of the fuel returning over the edge of a sharp machined surface in the FPR and producing the squeal, sort of like when air leaks out of a balloon through a small orifice.

Ed

That’s what I’ve beeen thinking. The noise is not new. It was there and more pronounced with the regulator at the end of the rail. I was hoping the plumbing changes would eliminate it. It’s a division X made by magnafuel.

I’ve called my turner. He said changes to what the injector sees could require a tune. Wants me to get a WOT AFR reading and let him know. Sensors bungs will be here today. Unfortunately, I won’t have time to weld them in until Sunday at the earliest.

Well I really didn’t plan on a re-tune, but it’s looking like that may be required. If that’s the case, the supercharger upgrade might be on the horizon.